Instrument Soceity Of India

Jl. of Instrum. Soc. of India

Vol. 39 No. 1

March 2009

A new experimental setup for measuring magnetostriction E.M. Mohammed1*, Suresh Babu M1, Neethal Thomas1 and P.J. Binu2 Department of Physics, Maharajas college, Ernakulam, Kerala, India - 682011 Department of Physics, St. Pius X College, Rajapuram, Kerala, India - 671532 * Corresponding author, E-mail:- [email protected]

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Abstract : One of the interesting phenomena associated with ferro and ferri magnetic materials is their magnetostriction. That is, these materials undergo a change in dimension when their state of magnetization is changed by an applied magnetic field. This paper describes one of the experimental setups for the accurate measurement of magnetostriction. We measured the magnetostriction of polycrystalline NiFe 2O4 samples with this setup and the results agree well with the standard values. This setup may be modified to be used as an optical modulator. Research using this setup can study the magnetostriction of different materials and to develop new devices for optical communication.

1. INTRODUCTION

2.2 Working

The history of magnetism dates back to earlier than 600 BC., but it is only in the 20th century that scientists have begun to understand it, and develop technologies based on it.

The sample under study is placed in the magnetic field as shown in figure 1. A laser beam from a Helium neon laser source is allowed to pass through an optical fiber attached to the sample. The light emerging from this optical fiber is made to fall on the detector after passing through another optical fiber. Before applying the magnetic field the two fibers should be aligned in such a way as to get the maximum intensity of light. According to the theory of magnetostriction, the application of a magnetic field will change the dimension of the sample.

One of the phenomena exhibited by ferro and ferri magnetic materials is magnetostriction [1, 2]. Ferromagnetic or ferrimagnetic material undergoes a change in dimension when its state of magnetization is changed by an applied magnetic field. The magnetostriction arises due to the magnetization change due to the rotation of the magnetization vector, or in other words, magnetostriction is mainly due to spin orbit coupling [3]. It is relatively weak because the applied field of a few hundred oersteds is required to rotate the spins away from the easy direction. Linear magnetostriction  is defined as  = l/l, where l is the original length of the specimen. l is the change in length. The effect is strongly dependent on the field strength. The value of  ranges from 10-6 to 10-4 for many substances. Some alloys of ferromagnetic metals and ferrites have high values of . Here we introduce a new experimental setup for the accurate measurement of magnetostriction. A setup for the studies of magnetic and optical properties of materials is fabricated using a magneto-optic sensor [4]. Using this setup the magnetostriction of different ferrite materials as well as the inter dependence of magnetostrictive constants on different physical conditions can be investigated.

Fig. 1. Schematic diagram of the sensor setup

The change in the dimension of the sample causes a change in the position of the optical fiber to which it is attached. As the position of the optical fiber changes, the intensity of the light reaching the detector changes. The display unit shows the intensity of the light reaching the detector. So, in each step, as we change the applied magnetic field the dimension of the sample changes. Correspondingly, the intensity value shown by the detector also changes. Thus, we can say that the strain produced is proportional to the change in the intensity of the light. By calibrating the detector output we can measure the strain produced in microns.

2. EXPERIMENTAL SETUP 2.1 Components of the setup For the accurate measurement of magnetostriction the setup needs the following components: electromagnet, optical fibers, detector, optical breadboard, laser unit and power suppliers. 23

E.M. Mohammed, Suresh Babu M, Neethal Thomas and P.J. Binu

3. RESULTS AND DISCUSSION

4. CONCLUSION

The raw materials used for the preparation of nickel ferrite are ferrous oxalate dehydrate (FOD) and nickel carbonate. The reaction involved in this process is

The NiFe 2 O 4 sample shows good magnetic properties. Here, the accent is on the study of its magnetostriction properties. An experimental setup for the accurate measurement of magnetostriction was used to study the magnetostriction of the nickel ferrite samples. The results are in good agreement with the standard values. The setup may be modified to be used as an optical modulator. Hence, research using this setup can continue to study the magnetostriction of different materials and to develop new devices for optical communication.

6(FeC2O4 2H2O) + NiCO3. 2Ni(OH)2 4H2O  3Ni Fe2O4 + 13CO2 + 9H2O + 9H2. The magnetostriction of nickel ferrite has been studied using the magneto-optic sensor setup as described earlier. Here, the strains produced in the nickel ferrite sample, corresponding to different field intensities are determined, and a graph is plotted with field in tesla and strain in microns (Fig. 2).

ACKNOWLEDGEMENT Dr. E M Mohammed acknowledges the Kerala State Council for Science, Technology and Environment for financial assistance (File No. 013/SRSPS/03/KSCSTE) and Suresh Babu M acknowledges the University Grants Commission for the financial assistance received under the fellowship.

REFERENCES 1. 2. Fig. 2. Magnetostriction of NiFe2O4 3.

Here, we can see that as the applied field increases, the strain produced in the sample also increases and finally the magnetostriction reaches a saturation value. No change in strain is produced on further increase of the field. The results tally well with the standard values [3].

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Smit J and Wijn H P G , ‘Ferrites’, The Netherlands, Philips Technical Library (1959). Mohammed E M, et al. ‘Tailoring Magnetic and Dielectric Properties of Rubber Ferrite Composites Containing Mixed Ferrites’, Bull. Mater. Sci., 6, 24, 623-631 (2001). Cullity B D, ‘Introduction to Magnetic Materials’, Philippines, Addison Wesley (1972). E M Mohammed and M R Anantharaman, ‘Fabrication of Conductivity Cell and Automation for the Measurements of Permittivity and ac Conductivity’, J. Instrum. Soc. India, 32, 3, 165–171 (2002).